Key aspects of digital colour theory
Understanding the practical use of colour for print production
CMYK V RGB
Cyan Magenta Yellow Key V Red Green Blue
Print V Screen
(Subtractive v additive)
Pigment V Light
Darker the more colour Brighter the more colours added
Limited colour Gamut V Wider colour Gamut
Paint & Print V Monitor, TV
Colour systems
Technical, essential knowledge to control your work
CMYK DEFINITION:
Stands for "Cyan Magenta Yellow Black." These are the four basic colors used for printing color images. Unlike RGB (red, green, blue), which is used for creating images on your computer screen, CMYK colors are "subtractive." This means the colors get darker as you blend them together. Since RGB colors are used for light, not pigments, the colors grow brighter as you blend them or increase their intensity.
RGB
SPOT COLOUR
Print technicians around the world use the term spot colour to mean any colour generated by a non-standard offset ink; such as metallic, fluorescent, spot varnish, or custom hand-mixed inks. (as opposed to obtaining a colour by via mix of cmyk)
Spot colour
GREYSCALE
One colour black and all the shades of grey through to white (black and white photography is grey scale)
Grayscale
MONOCHROME (mono)
Like grayscale but with coloured ink ie one colour and % tints of that colours plus the colour of the material it's printed on.
Monochromatic colours are all the colours of a single hue derived from one colour and extended using the shades,tones and tints of that colour.
Mono
DUOTONE
Duo
When a continuous tone image is printed in 2 or more spot colours. This term is also generally used when describing tri and quad colours.
HALFTONE
This is a mechanical process (as opposed to chemical) for converting tonal values into a series of dots that although solid dots, when printed give the impression of continuous tone.
Rich Black
richblack_vs_plainblack
Black on screen - 0 R 0 G 0 B
Printing black
plain black/ 100% black ink 0C, 0M, 0Y, 100K
Rich black - printing other inks along with black.
Most common
rich black 63C, 52M, 51Y 100K.
This particular variant owes it's popularity to Adobe Photoshop - when an RGB file is converted to CMYK, areas that are absolute RGB black (R0, G0, B0) will wind up with this combination, unless certain default settings have been changed.
Cool Black 60C, 0M, 0Y, 100K
Warm Black 0C, 60M, 30C, 100K
Important to remember although all black looks the same on screen ie RGB they will not look the same printed out. Always ensure using a consisitant mix of black throughout a document/image.
The special-purpose color "registration" is another potential source of black mismatches. On screen, by default, it appears as R0, G0, B0, so it seems as if it might be the same as black. It's not. Registration color prints 100% on all plates. If your layout is CMYK, then registration color is 100C, 100M, 100Y, 100K. If your layout is CMYK + Pantone 285, then registration color is 100C, 100M, 100Y, 100K, 100Pantone 285. Registration color is used for, appropriately enough, registration marks, explained elsewhere. Do not use it in place of black. Having that much ink go down presents many problems from a printing standpoint.
Don't use Rich Black for Text use plain black. If the printer has registration problems the text could become difficult to read
Other tips picked up from Lorenzo's links:
For accurate colour matching use Pantone Colours so what you see is what you get rather than trying to match a colour you like on screen.
Check with your printer what type of files they prefer. PDF is good because they are smaller file sizes than Photoshop or Illustrator.
The Problem
Using the wrong resolution in your works can be detrimental to your final outcome. It is important to know the final destination of your work so that you can design at the correct resolution. Most printers print at about 300dpi (dots per inch), some even at 600dpi or above. The resolution of a monitor is 72ppi (pixels per inch), and is a default setting in Photoshop and Illustrator for RGB design.
A few things to note…
So let’s talk about some basic differences between dpi and ppi, and then decide what is best to use for different projects.
Simply put, pixels are square, dots are… well, dots. They consist of one color. Obviously, the more dots or pixels per inch, the more detailed and accurate your picture will be. It is important to design at 300ppi so that when you print on a 300 dpi printer, each pixel is translated as a dot. It is okay to design at a higher ppi than your printer’s dpi, but be careful designing below 300ppi.
The Fix
Unless you are designing something huge, the magic number for print design is… you guessed it,300dpi. Generally, anything that you can hold in your hands should be designed at or above 300dpi. It is especially important to note that though you can go down in dpi, you cannot go up without quality loss (when working with rasterized elements). Therefore, as long as your processor can handle it, it is best practice to work at 300 dpi or the maximum for your specific printer.
Depending on the size of a particular piece, you may have to design for perspective resolution. In other words, a billboard, from the road, appears to be a couple of inches wide, so therefore the dpi can be much lower (often around 18-20 dpi).
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